As a surface treatment for improving the hardness and so on of an iron-based metal material, a carburization process where carbon atoms are dissolved up to a depth in the range of several tens micrometers to several millimeters from a surface is generally applied. As a carbon source thereof, in a solid carburization process, wood charcoal, graphite or the like is used, and, in a gas carburization process, a hydrocarbon gas, a natural gas or the like is used. However, in the solid carburization process, there is a problem in that, because a carbon source is low in the reactivity, it is necessary to heat over a rather long time at such a high temperature as 900° C. or more during the carburization and thereby metal grains become coarse to tend to deteriorate in the mechanical strength. On the other hand, the gas carburization process, though suitable for mass production, has a problem in that expensive apparatus is necessary.
Now, fullerene is a spherical molecule made of only carbon atoms, has a magnitude of one molecule of substantially 1 nm and is gathering attention because of high reactivity. The reason why the fullerene is high in the reactivity is in that, while other carbon materials such as graphite and the like are made of a fundamental structure that has relatively stable six-membered rings of carbons, the fullerene has five-membered rings higher in the reactivity other than the six-membered rings. Accordingly, in recent years, various studies are in progress of reactions between fullerene and organic compounds or the like.
As to a reaction between a metal and fullerene, for instance, patent literature 1 discloses that owing to a reaction between the outermost surface of a metal such as titanium or the like that tends to form a carbide and fullerene, a carbide containing fullerene is formed.    Patent literature 1: JP-T No. 2002-538906
Furthermore, the fullerene is a spherical molecule made of only carbon atoms and having a magnitude of one molecule of substantially 1 nm. The fullerene, not containing oxygen, hydrogen and nitrogen in a molecule, does not generate a pyrolysis gas even when it is heated to 300° C. or more. Furthermore, since the fullerene has, other than six-membered rings, five-membered rings high in there activity in a molecule, fullerenes, when heated, react with each other to form amorphous carbon. The formation of amorphous carbon is a phenomenon that is peculiar to the fullerene and cannot be found in other carbon materials such as graphite and so on.
As supposed from these, when a film made of fullerene is heated, without generating a pyrolysis gas, a dense amorphous carbon film made of only carbon is formed. The carbon film, having excellent properties such as the lubricity and so on, is a material useful in various kinds of applications including surface protection of a material and so on.
However, since, when a fullerene film is formed, usually, expensive apparatus such as a vacuum deposition device is necessary and since a thick film is very difficult to be formed, carbon films are not industrially produced from fullerene films.
As another general method of forming a film, there is a method called a thermal spraying method. In the thermal spraying method, powders of metal, ceramics or the like are heated to a high temperature to melt and adhere to a surface of a material to form a thick film. The thermal spraying method is an industrially very useful film-forming method. However, until now, a carbon material film obtained by the thermal spraying method is limited to a nickel-graphite thermal sprayed film. This is because a general carbon material such as graphite or carbon black lacks the crystallinity and does not melt and thereby a film cannot be formed by use of the thermal spraying. Furthermore, for ones familiar with a field of the thermal spraying, since the fullerene sublimates or burns under a high temperature, it is technical commonsense that the fullerene is not suitable for the thermal spraying.
On the other hand, it is proposed to prepare a film containing fullerene by means of the thermal spraying method. That is, patent literature 2 proposes to form, by a thermal spraying method, a coated film in which nanocarbons including fullerene are dispersed.    Patent literature 2: JP-A No. 2005-29873